Polybutylene terephthalate resin is used in a wide range of fields, such as automobile parts, electric/electronic parts due to the excellent mechanical properties, electric properties, and other physical and chemical properties, along with good workability. In particular, since its heat resistance and strength can be improved by adding a fibrous filler such as glass fiber thereto, the polybutylene terephthalate resin is often used as a polybutylene terephthalate resin composition reinforced with the fibrous filler.
Although the polybutylene terephthalate resin has excellent properties as described above, being a polyester resin, it also has a disadvantage that the physical properties are easily impaired according to hydrolysis. In this connection, it is well known that the hydrolysis resistance can be improved by adding a carbodiimide compound to the polybutylene terephthalate resin.
In particular, the polybutylene terephthalate resin composition having modified physical properties according to addition of a fibrous filler or a carbodiimide compound is often used as a material of a housing for a sensor or an engine control unit, which is used for electric control in the automobile field. When the product used for such purpose is an insert molded article, it is used under an environment of severe temperature increase and decrease, such as engine room of automobile, and therefore a crack may be easily caused by deformation resulting from the difference in linear expansion between a metal insert and the polybutylene terephthalate resin. For such reasons, a product used for such purpose is required to have heat shock resistance for prevention of crack generation that is caused by a severe difference in temperature. The product used for such purpose is sometimes also required to have high flame retardancy.
In an electric automobile field, in particular, it is believed that the flame retardancy is often required as well the durability that has been generally regarded necessary in the automobile field.
In consideration of the circumstances described above, studies have been made for inhibiting crack generation that is caused by heat shock due to severe temperature increase and decrease. For example, a polybutylene terephthalate resin composition in which acrylic rubber, an epoxy compound, pentaerythritol ester, a fibrous reinforcing agent, and a carbodiimide compound are added is suggested (Patent Literature 1).    [Patent Literature 1] Japanese Patent Application Laid-Open (JP-A) No. 63-003055